As used in the following disclosure and claims, the term polycrystalline diamond (PCD) is intended to refer to the type of material that is made by subjecting diamond crystals to a high temperature and pressure that results in intercrystalline bonding of the individual diamond crystal. In exemplary embodiments, the intercrystalline bonding is usually facilitated by use of a specific catalyst family of transition metals, usually as molten fluid. Although catalysts greatly aid the sinter bonding of PCD, it is frequently the case that catalyst is left over in the PCD material. This is especially true for diamond granular materials that are difficult to contact with molten metals, such as fine particle size and/or highly textured diamond. The presence of residual catalyst in the PCD generally changes its quality and compels design compromise between various desirable and undesirable properties of a cutting material. PCD is not diamond; it is a composite of varying composition comprising hard diamond and soft catalyst metal.
In many different applications, PCD has displayed advantages over the use of a single crystal diamond. Typically, a single crystal diamond has a much lower impact resistance than PCD, due to the much higher modulus of elasticity of a single crystal compared to PCD. Furthermore, the specific planes of cleavage of a single crystal may allow relatively low forces to cause fracturing of the crystal. However, PCD may alleviate the problems caused by the planes of cleavage of a single crystal because the PCD is made up of randomly oriented individual crystals.
In some cases, PCD have been used for many years in drilling and machining. In the drilling industry the Polycrystalline Diamond Composite products are typically brazed to the drill bits is referred to as PDC. Therefore, from this point on when referring to Polycrystalline Diamond Composite used in the drilling industry, PDC is the abbreviation that will be used and it means the same thing as PCD.
Known PDCs have drawbacks that lead to the degradation wherein the PDC is unable to cut rock or stone. One of the factors limiting the success of the PDC is that larger crystals that may be used to form the PDC, while easy to sinter completely with low residual catalyst, typically produce fewer diamond-to-diamond bonds per unit volume. Fewer diamond-to-diamond bonds per unit volume may mean a weaker PDC. However, the lower residual catalyst content improves thermal resistance of PDC. Residual catalyst metal expands far more than sintered diamond and tends to weaken the PDC. Friction heat in all machining can be very high regardless of many methods used to mitigate it. Thus, larger grain size PDC has a tendency to fracture and abrade more easily than PDC comprising a multitude of smaller crystals but is more capable of withstanding heat.
On the contrary smaller crystals can generate more diamond-to-diamond intergranular bonds per unit volume but are more difficult to sinter completely to low residual catalyst metal content. Thus, finer grain size PCD tends to have higher hardness and strength but also higher residual catalyst content. Higher residual catalyst lowers density of diamond-to-diamond bonds, catalyst taking the space diamond would otherwise, but more importantly lowers the heat tolerance of PDC.
The result is a range of grades of PDC representing the compromise of hardness and heat resistance achieved by coarse and fine grains, with varying residual catalyst content, which perform non-optimally. Hard PDC is more sensitive to heat; heat-tolerant PDC is soft.
The different regions of the cutter perform different functions and optimally need not be the same material. In some embodiments, the rake may resist thermal spalling, chipping and adhesion wear, and be hard to resist abrasion of loose rock debris sliding over it. In exemplary embodiments, the flank may be very hard to grind the hard rock surface. The edge should be strong and hard. Therefore, it may be advantageous to use a multitude of smaller crystals in areas that need enhanced abrasion resistance, larger crystals in areas to enhance higher thermal resistance and/or different compositions of PDC to better handle the overall cutting function.
PDC have been used for industrial applications including rock drilling and metal machining for many years. PDC is normally bonded to a substrate, typically sintered tungsten carbide, to make shaping of the cutter and attachment of the cutter to a tool, such as a drill, easier. PDC is very difficult to machine and attach to common drill materials, like steel or infiltrated carbide-metal. Sintered tungsten carbide is easy to machine and attach to metal drill bodies and toolholders, via for example, brazing.
Of course one of the factors limiting the success of PDC is the strength of the bond between the polycrystalline diamond layer and the cemented tungsten carbide substrate. For example, analyses of the failure mode for drill bits used for deep hole rock drilling show that in approximately thirty-three percent of the cases, bit failure or wear is caused by delamination of the diamond from the metal carbide substrate.
Furthermore, when cemented carbide mass is relied on to increase the impact resistance of PDC, the diamond layer is preferably relatively thin so that the diamond behaves as a supported layer, rather than monolithically. This restriction on the thickness of the diamond layer limits both the life expectancy of the composite body in use as well as the designs for PDC diamond tools.
Yet another problem that has limited the thickness of the diamond layer in composite bodies is caused by the problem of “bridging”. Bridging refers to the phenomenon that occurs when a fine powder (especially a mono-modal powder) is pressed from multiple directions. It is observed that the individual particles in a powder being pressed tend to stack up and form arches or “bridges” that block the full amount of pressure so that the pressure often does not reach the center of the powder being pressed. This results in high porosity which requires more catalyst and thus tends to leave more residual catalyst in the sintered PDC.
In any type of PDC, there are two countering principals that are opposed to one another. For optimal abrasion resistance, very fine crystals of the abrasive material are used. The fine abrasive materials are sintered under high pressure and result in a higher density compact with more diamond-to-diamond bonds than coarser material in the PDC. However, as a result of the high density, the abrasive mass of very fine crystals presents increased resistance to the catalyst metal or catalyst metal and carbide from sweeping through the crystal interstices as well as increased packing defects due to bridging. The increased resistance may lead to soft spots of non- or weakly bonded abrasive material in the PDC.
However, coarser and/or larger abrasive crystals may provide larger channels and spaces in the compacted mass that may allow the catalyst metal to sweep through. Additionally, coarser and/or larger abrasive crystals may provide larger impact resistance when compared to smaller crystals, due to the higher content of catalyst metal. On the other hand, coarser materials may not provide the abrasion resistance that may be desired for a PDC material since they do not produce high diamond-to-diamond bonds per unit volume of PDC.
While grain and packing artifacts affect the quality of the PDC sintered mass, it also affects the quality of the bond of the PDC to the substrate. That bond is made by filaments of metal intermingled between sintered tungsten carbide and the PDC body. The higher the number per unit area of metal filaments penetrating both PDC and substrate, the better the bond. This is typically optimized by fine diamond grains adjacent to the substrate. Nonetheless, the issues of pressure and compaction affect this region of PDC perhaps more so than the PDC body.